1. Field of the Invention
This invention relates to floating equipment used in cementing operations and to methods of fabricating such equipment. More particularly, this invention relates to an improved floating apparatus that provides for improved reliability to hold differential pressures under a variety of cyclic loading conditions.
2. Description of the Related Art
Typically, after a well for the production of oil and/or gas has been drilled, casing will be lowered into and cemented in the well. The weight of the casing, particularly with deep wells, creates a tremendous amount of stress and strain on the equipment used to lower the casing into the well. In order to minimize that stress, floating equipment, such as, but not limited to, float shoes and/or float collars are used in the casing string. Typical of the float equipment that might be used is the Halliburton Super Seal™ II float collar and the Halliburton Super Seal™ II Float Shoe.
The float equipment typically consists of a valve affixed to the outer casing which allows fluid to flow down through the casing but prevents flow in the opposite direction. Because upward flow is obstructed, a portion of the weight of the casing will float or ride on the well fluid thus reducing the amount of weight carried by the equipment lowering the casing into the well.
Once the casing is installed into the wellbore, cement fluid is commonly pumped from the surface through the casing into the wellbore at the lower end of the casing. The cement is lifted up the annulus with pressure pumping equipment because the weight or density of the cement is generally greater than the weight or density of the displacement fluid pumped behind the cement. After displacement operations are completed, the casing is filled with displacement fluid and cement is located in the annular space between the casing and the wellbore for the purpose of creating annular isolation, at which point the surface pressure is released and the valve holds the cement in place by creating a barrier for holding differential pressure.
The float equipment is typically fabricated by affixing a check valve in an outer sleeve, which is adapted to be threaded directly into a casing string. The valve is affixed by filling the annulus between the valve housing and the outer sleeve with a high compressive strength cement to form a cement body portion. Over a period of time, the cement poured between the valve and the outer sleeve shrinks slightly as it cures. The shrinkage can cause a micro-annulus between the cement body portion and the outer sleeve and between the cement body portion and the valve. Fluid flowing through the casing can flow through the micro-annulus thus eroding the cement body portion and causing a leak. The leakage through the micro-annulus will allow the cement used to cement the casing in place to re-enter the inner diameter of the casing after the cementing job is completed. The cement must be removed by drilling. The leakage will also allow well fluids to contaminate the cement on the outer diameter of the casing, which affects the integrity of the cement and the cementing job.
Additionally, recent events in the industry have increased the focus on performance testing of cementing float equipment. Specifically, API Standard 65-2 and API RP 10F have elevated the performance testing requirements of cementing float equipment. Current float designs are scarcely able to pass the rigorous testing described.
Accordingly, it is important that there be a competent bond between the cement and the valve and between the cement and the casing, which avoids leakage so that the bonds provide the desired hydraulic pressure rating and hold the needed differential pressure. Accordingly, it would be advantageous to improve the bond between the cement and the case and between the cement and the valve.